The present application claims priority under 35 U.S.C. xc2xa7119 of German Patent Application No. 199 34 875.8, filed on Jul. 24, 1999, the disclosure of which is expressly incorporated by reference herein in its entirety.
1. Field of the Invention
The invention relates to a machine for producing and/or finishing a fibrous material web having a press section for the dewatering thereof, a former for sheet formation situated before it, and a dryer section for drying the fibrous material web disposed after it.
2. Discussion of Background Information
Such machines are described, for example, in EP 770 727, in which the fibrous material web is guided through at least two elongated press nips of the press section jointly with multiple press felts. Because the fibrous material web in the press nips comes into contact with various press felts, irregularities in the ability to absorb water or the moisture content of the press felts observed crosswise to the fibrous material web can be better compensated. The result is that the moisture cross profile of the fibrous material web is relatively uniform.
The disadvantage here is the large space requirement and the relatively high expense of producing the two elongated press nips, which are formed in conjunction with relatively expensive shoe press rolls.
The object of the invention is therefore to create a paper machine having a press section that is as small but as efficient as possible and that involves the lowest possible cost.
This object is attained according to the invention in that the press section comprises only one press nip formed by two press rolls, through which, next to the fibrous material web, disposed on both sides thereof, at least one press felt is guided, the fibrous material web is dewatered in the former to a dry content of at least approximately 18%, preferably at least approximately 20%, the first dryer group of the dryer section includes a maximum of three heated dryer cylinders, which are partially looped around by the fibrous material web, and the fibrous material web is supported constantly from the former to the end of the first dryer group by at least one roll or one belt in the form of a former screen, a press felt, a transfer belt, or a dryer screen.
The dry content after the former of at least approximately 18%, preferably at least approximately 20%, allows the limitation to only one elongated press nip in the press section. However, due to the relatively high moisture content of the fibrous material web after the press nip, closed guidance of the fibrous material web from the former is important, in particular up to the end of the first dryer group, especially at high machine speeds. Moreover, stretching of the fibrous material web, even as a result of the high moisture content at the beginning of the dryer section, must be compensated as quickly as possible, which is why at least the first dryer group is designed to be as short as possible. Otherwise, the risk would arise of tearing the web or the formation of folds. Compensation for the stretching is generally achieved in that each subsequent dryer group is operated at a higher speed than the preceding one.
To ensure sufficient dewatering in the press nip, the length of the press nip should be greater than approximately 300 mm, preferably greater than approximately 500 mm. In order to guarantee sufficient pressing time, the web speed here should not exceed approximately 1,500 m/min. In addition, the line force in the press nip should be above approximately 800 KN/m, preferably above approximately 1,000 KN/m, and in particular above approximately 1,200 KN/m. That allows pressure impulses of more than approximately 60 KPa s to be achieved. However, because those values are subject to upper limits from the viewpoint of mechanical engineering and cost, as well as the strength of the press felt, use appears particularly appropriate for producing fibrous material webs having a basis weight between approximately 50 and 200 g/m2, preferably between approximately 50 and 100 g/m2, and/or producing wood-free paper webs. In all other cases, the requirements for the press section would be relatively high, but also feasible.
To guarantee a constant dry content of at least approximately 18%, preferably at least approximately 20%, at least one suction device that suctions the water from the fibrous material web through the former screen should be disposed in the former before the transition point of the fibrous material web onto the press section. However, it is also possible, in combination or alone, for the fibrous material web to be guided jointly with at least one endless circulating water-absorbent or water-permeable belt through a pre-press nip that is preferably formed by two rolls in the former before the transition point of the fibrous material web onto the press section. In the case of the combination, i.e., when the pre-press nip is formed by two rolls in the form of a suctioned roll and a press roll, the former screen should loop around the suctioned roll as a water-permeable belt.
To receive the water pressed out in the pre-press nip, at least one roll in the form of a press roll should also be looped around by a water-absorbent belt in the form of a press felt.
Moreover, a moistening device, preferably in the form of a steam blower box to act on the moisture cross profile of the fibrous material web, should be present in the press section before the press nip. Therefore, it is possible for the uniformizing effect of multiple press nips within the press section not merely to be achieved, but also to be exceeded. For that purpose, at least in the press section or in a subsequent unit, sensors that act on at least the moistening device should be disposed to record the moisture cross profile of the fibrous material web. The results of those sensors can also be used to control the suction device and/or the pressure force in the pre-press nip in the former. However, this requires at least the moistening device, but preferably also the suction device and/or the pressure force, to be controllable separately in zones crosswise to the fibrous material web.
Because a great deal of water is present in the single press nip of the press section, the fibrous material web should leave the press nip horizontally or slanted downward, and a channel to collect the water spun off by the upper press roll should be disposed at least over the upper press felt.
In addition, as described above, at least the first dryer group should be very short, preferably formed by a maximum of two, in particular by a maximum of one, heated dryer cylinders.
The present invention is directed to a machine for at least one of producing and finishing a fibrous material web. The machine includes a press section, for dewatering the fibrous web, with a press nip, a former, located before, relative to a web travel direction, the press section for sheet formation, and a dryer section, located after the press section for drying the fibrous material web including a first dryer section having no more than three dryer cylinders. Two press rolls are arranged to form the press nip, and at least one press felt is located on each surface of the material web, such that the material web and the at least one press felt on each side of the material web are guided through the press nip. The fibrous material web is dewatered in the former to a dry content of at least approximately 18%, partially loops around the no more than three dryer cylinders, and is constantly supported from the former to an end of the first dryer group.
In accordance with a feature of the invention, the dryer section can include only one press nip. Further, the fibrous material can be dewatered in the former to a dry content of approximately 20%, and the material web may be constantly supported by at least one of a belt and a roll.
According to another feature of the present invention, a length of the press nip may be greater than approximately 300 mm, and preferably the length of the press nip may be greater than approximately 500 mm.
In accordance with another feature of the instant invention, a line force in the press nip can be above approximately 800 KN/m, preferably above approximately 1,000 KN/m, and most preferably above approximately 1,200 KN/m.
Further, the machine may include at least one suction device located in the former and before a point at which the fibrous web is transferred to the press section. The at least one suction device can provide a dry content of at least approximately 18%. Further, the at least one suction device provides a dry content of at least approximately 20%.
The former may include a pre-press nip having two rolls and at least one endless belt guided through the pre-press nip. At a point before the fibrous material web is transferred to the press section, the fibrous material web can be guided jointly with the at least one endless belt through the pre-press nip. The at least one endless belt may include at least one of a water-absorbent and a water-permeable belt. The two rolls of the pre-press nip can include a suctioned roll and a press roll, and the endless belt can include a former screen looping around the suctioned roll. The two rolls of the pre-press nip can include at least one press roll, and the endless belt can include a press felt looping around the at least one roll.
According to a further feature of the invention, the press section can further include a moistening device positioned before the press nip adapted to influence a moisture cross-profile of the fibrous material web. The moistening device can include a steam blower box. Further, sensors can be adapted to record the moisture cross-profile of the fibrous material web. The sensors can be coupled to the moistening device and can be located in at least one of the press section and the dryer section. The former can include a pre-press nip and a suction device, and the sensors may be coupled to at least one of the pre-press nip and the suction device.
In accordance with a still further feature of the present invention, the fibrous material web may leave the press nip one of horizontally or slanted downwardly, and the machine can further include a channel to collect the water spun off by an upper press roll, which is located at least over an upper press felt.
Further, the first dryer group can include no more than two heated dryer cylinders. Moreover, the first dryer group can include only one heated dryer cylinder.
A basis weight of the fibrous material web being produced can be between approximately 50 and 200 g/m2, and preferably the basis weight is between approximately 50 and 100 g/m2.
In accordance with still another feature of the instant invention, the fibrous material web can include wood-free paper.
According to still another feature of the present invention, web speed may not exceed approximately 1,500 m/min.
The present invention is directed to a process for at least one of producing and finishing a fibrous material web in a machine that includes a former, a press section, and a dryer section. The process includes dewatering the fibrous material web in the former to dry content of at least approximately 18%, dewatering the fibrous material web in only one press nip in the press section, and looping the fibrous material web around no more than three dryer cylinders in a first dryer group of the dryer section a dryer section. The fibrous material web is constantly supported between the former and an end of the first dryer group.
According to a feature of the invention, the fibrous material can be dewatered in the former to a dry content of approximately 20%.
In accordance with yet another feature of the present invention, the process can further include pre-pressing the fibrous material web in the former in a pre-press. The process can also include measuring a moisture cross-profile of the fibrous material web with sensors located in at least one of the press section and the dryer section, and moistening the fibrous material web before, relative to a web travel direction, the one press nip in the press section. The sensors may be coupled to adjust the pre-press. The pre-press can include a suction device, and the sensors may be coupled to adjust the suction device.
Other exemplary embodiments and advantages of the present invention may be ascertained by reviewing the present disclosure and the accompanying drawing.